Biodiesel is gaining growing acceptance as a diesel fuel component. “Biodiesel” typically comprises fatty acid esters made from vegetable oil triglycerides, which can include various crops or waste oil, or other animal fats. Algae sources can also yield suitable triglycerides. The raw vegetable oil or animal fat triglycerides are reacted with alcohols such as methanol to form fatty acid alkyl esters specifically to attain a viscosity within the diesel specification. A common type of fatty acid alkyl ester is fatty acid methyl ester, or FAME. A separate ASTM specification has issued that covers Biodiesel (D6751-07) when blended with conventional diesel, but some of the specifications are not consistent with conventional diesel specifications required for the mixed blend. For example, the biodiesel Cloud Point specification is shown as “report only”, with a footnote that it is usually higher than conventional diesel fuel and that this need to be taken into consideration. Biodiesel fuels often have relatively high cloud points. As a result, blends of biodiesel and conventional diesel may render the total blend unsuitable in terms of cloud point and/or other cold flow properties.
European Patent Application Nos. EP 1741767 and EP 1741768 each describe methods for hydroprocessing diesel range feeds based on biocomponent sources, such as vegetable or animal fats/oils. The hydroprocessing methods include exposing the biocomponent feed to hydrotreating conditions, followed by a hydroprocessing step for isomerizing the feed. Isomerization catalysts identified in these publications include SAPO-11, SAPO-41, ZSM-22, ZSM-23, and ferrierite. The isomerization catalysts are described as also including a Group VIII metal such as Pt and a binder such as alumina. The lowest cloud points identified in the references are between −14° C. and −22° C. The levels of n-paraffins remaining in the isomerized diesel products were not specified.
U.S. Published Patent Application No. 2007/0006523 describes methods for producing diesel fuels from a Tall Oil Fatty Acid (TOFA) fraction. The TOFA fraction is described as including triglycerides present in biocomponent feeds, such as rapeseed oil, sunflower oil, or palm oil. The methods include hydrotreatment, followed by isomerization. The most suitable isomerization catalysts are described as catalysts with low acidity. SAPO-11 bound with alumina and ZSM-22 or ZSM-23 bound with alumina are provided as examples of isomerization catalysts. The isomerization catalyst is also described as including a supported Group VIII metal such as Pt. No cloud points are provided for the diesel fuel products. The lowest reported number for the amount of n-paraffins in an isomerized product is 13%.
U.S. Published Patent Application No. 2006/0207166 describes methods for hydroprocessing biocomponent feeds in a single step. The single step performs both hydrodeoxygenation and hydroisomerization. The catalyst for the single step is described as including both a metal component and an acidic component. The metal component is described as platinum or palladium. A wide variety of zeolites are described for the acidic component. A porous solid support may also be present. The lowest cloud points reported for diesel fuels made according to the process described in this publication are between −11° C. and −16° C. A cloud point below −20° C. is also reported in a comparative example. After processing, the reported diesel products had n-paraffin contents of at least 14.5%.
U.S. Published Patent Application No. 2009/0019763 describes a method for treating mixtures of vegetable oil and mineral feed with a catalyst under hydrotreating conditions. The catalyst can include cobalt and molybdenum supported on a dealuminated form of ZSM-5.
International Application No. PCT/US2008/012516 describes methods for treating a biocomponent feedstock by first hydrotreating the feed and then dewaxing the feed under catalytic dewaxing conditions. The dewaxing catalyst can be a ZSM-48 containing catalyst that includes platinum.
What is needed is a method for producing biocomponent based diesel fuels with improved properties to facilitate use in the commercial fuel supply. Preferably, the method would allow for production of diesel fuels that satisfy any current cold flow property requirements while also providing improved cetane.